Pre-baby boomers were the least stressed at only 7.9 per cent.
"A wide range of factors can contribute to stress, including work, finance, health and family matters," said Roy Morgan general manager Pip Elliott.
"In terms of how this has changed historically for the North and South Island, the biggest increase was among those who live in the South Island, increasing from 16.5 per cent in 2011 to 19.4 per cent in 2012."
Yet despite the marked increase in stress for the South Island, Roy Morgan said it wasn't willing to attribute the results to the Christchurch earthquakes.
"We didn't make that link, that's something that would be more speculative than hard concrete data," said senior account manager Jon Hackett.
"We don't ask for the source of the stress in the interviews but you can speculate.
"That could very well be the case - financial stress due to the quakes."
He said women in Australia were also much more likely to suffer stress than men and Australians living in the country were more likely to suffer stress than those in the city.
Roy Morgan interviews an average of 12,000 New Zealanders over the age of 14 every year, 48 weeks a year.